Introduction
Retrieving devices are commonly used for training hunting canines to retrieve downed game, and are commonly referred to “bumper bars” or just “bumpers.” Conventional bumpers come in two basic designs: traditional cylindrical dummies and dead fowl dummies. Cylindrical dummies are solid-walled objects made of rubber, plastic, or canvas, typically about 12 inches long and about 1 to 4 inches in diameter. Dead fowl dummies are solid-walled objects shaped and painted to resemble deal fowl. In use, a trainer launches a bumper out to a spot as much as about 800 yards away from a dog, and the dog retrieves the bumper while holding the bumper in its mouth, then the launch-and-retrieve process is repeated a number of times during a training sessions.
Repeatedly retrieving a bumper during a training session is rigorous exercise for a dog. During such exercise, dogs can produce heat at a rate about 50 to 80 times higher than their resting metabolic rate, and their oxygen uptake can be increased up to about 15 times its resting value. Some researchers have reported that in order for dogs to compensate for the increase in heat production and oxygen uptake, dogs increase their respiratory rate from about 36 breaths per minute (bpm) to over 270 bpm. When a dog is under heat stress, its respiratory airflow path changes so that inhalation and exhalation occur through the mouth in addition to through the nose to increase its ventilatory rate and capacity. Evaporation from the upper respiratory tract constitutes the primary means of heat loss for dogs when they are under heat stress. Researchers have shown that dogs are able to increase heat loss by exhaling primarily through the mouth, where two of the major three (nasal, buccal, and lingual) evaporative surface areas are located.
Conventional bumpers retard the ability of the buccal (mouth) and lingual (tongue) surface areas to participate in thermoregulatory evaporation mechanisms. This is because when a dog holds a bumper in its mouth, the dog's lips tend to form a seal around the bumper, thereby restricting airflow over the buccal and lingual surface areas. In particular, the lips seal around the bumper to block airflow through the sides of the dog's mouth and through most of the front of the mouth, with the tongue filling most of the bottom gap between the bumper and the bottom of the mouth and with only the circuitous top passageway/gap between the bumper and the roof of the mouth unobstructed for airflow. One such conventional bumper 10 is shown in FIG. 1, with FIG. 2 showing the same bumper held in a dog's mouth restricting airflow through the mouth to only that top portion of the mouth between the bumper and the roof (as indicated by the directional arrows). In addition, because conventional bumpers significantly block airflow through the dog's mouth during retrieving activities, their use can decrease gas exchange, and can increase cardiac output, intra-thoracic pressure, and psychological stress. As a result, when retrieving conventional bumpers, dogs are subject to overheating (thermal stress), cardiopulmonary stress, and psychological stress.
Heat Exchange
The onset of panting is marked by a change from closed-mouth (breathing through the nostrils only) to open-mouth respiration (additionally breathing through the mouth), and by a sudden increase in the respiratory frequency from about 36 bpm to as much as about 270 bpm. Researchers have found that panting is responsible for most of the heat loss by dogs, and that most of that heat loss occurs in the mouth during panting, and accordingly that breathing through the mouth is an important thermoregulatory mechanism during canine exercise. High body temperatures are associated with high rates of blood flow in the nasal passages, oral passages, and tongue, areas that are being cooled by evaporation. Also, research studies involving blood flow have shown that when a dog's body is heated, blood flow to the nose, mouth, and tongue rises as breathing frequency increases. Studies have revealed that when a dog is under thermal stress, salivation and lingual blood-flow increases dramatically. In addition, lingual arteriovenous temperature differences increase during thermal stress, which indicates that heat is being lost. Studies on dogs exercising in the heat have shown that the rate of respiratory evaporation is related to the elevation in body temperature. That is, if the rate of respiratory evaporation decreases, body temperature increases.
The main mechanism for heat exchange in dogs to keep their brains cool includes in a small network of arteries, called the carotid rete, which is surrounded by venous blood that drains the nasal and oral passages. Warm blood in the arteries loses heat to the venous blood, which is cooled by evaporation in the nose and mouth. When dogs are panting, evaporation from the nose and mouth is increased and the brain is kept cooler than other deep-body regions. Since the brain is sensitive to and adversely affected by overheating, and thermoregulation at the level of the carotid rete is important for cooling of the brain, it is important that dogs be allowed to pant freely and that air be allowed to flow freely over the major evaporative surfaces of the mouth.
The increase in respiratory evaporative heat loss during exercise may be due to the change in the pattern of breathing as well as the increased ventilation rate. The changed pattern of breathing is inhalation and exhalation through both the mouth and nose (instead of just through the nose). The recruitment of the additional evaporative surface of the mouth during exercise may explain part of the increased evaporative heat loss. Venous blood draining from the oral and nasal cavities can drain into the cranial cavity, where it comes in close contact with cerebral arterial blood. Researchers have found that the acceleration of respiratory evaporation during exercise, which would lead to maximum cooling of the nasal and oral venous blood, allows a high rate of heat exchange in the carotid rete of the dog and significant cooling of the brain. In addition, normal brain functions start to become disturbed at temperatures of about 4 C above normal, and cooling the brain more than about 1 C below the temperature of the blood in the body core could increase a dog's exercise tolerance significantly. In other words, not only does hyperthermia endanger brain function, it's also a limiting factor to canine performance.
Gas Exchange
During strenuous exercise, a dog's oxygen uptake can be increased up to about 15 times its at-rest value. Gas exchange is important for waste removal from, and oxygen delivery to, working muscles. Conventional bumpers significantly obstruct the upper airway system and decrease the dog's ability to inhale and exhale efficiently. In addition, conventional bumpers retard the dog's ability to use natural breathing patterns through the nose and mouth. This can decrease gas exchange and thereby increase the onset of fatigue and increase psychological stress.
Cardiac Output and Intrathoracic Pressure
Dogs exercising at workloads of about 4 to 10 times the resting metabolic rate in relatively hot environments have higher cardiac outputs than dogs exercising in cooler environments. The increment in cardiac output in dogs exercising in the heat can be accounted for by increased rates of flow to the respiratory muscles and the evaporative surfaces of the nose, mouth, and tongue. Increased blood flow to the respiratory muscles probably accounts for most of the elevation in cardiac output. This is because of the mass of the respiratory muscles and their increased blood flow during panting. The increase in blood flow to the respiratory muscles is to facilitate oxygen delivery and waste removal from these muscles as they work to force the lungs to exchange air with the environment. The exchange of air facilitates body heat and carbon dioxide removal as well as oxygen intake. During moderate-to-strenuous exercise, a dog's pant rate can increase to over 200 times per minute (over 3 times per second). And researchers have found that with heat stress not only does panting frequency increase, but also the intensity of panting increases (measured by the amplitude of intrathoracic pressure variations). This means that conventional bumpers increase intrathoracic pressure by forcing the dog to push large volumes of air through the small airways of the nostrils and adjacent the roof of the mouth instead of the larger airway of the mouth (the larger the airway, the less force required to exhale and inhale through it). In addition, this may cause the respiratory muscles to increase force output, burn more energy, increase oxygen demand, and increase heat production in the thoracic cavity. In order to meet these demands, the strain on the cardiovascular system significantly increases. Thus, the use of conventional bumpers increases the thermal, respiratory, cardiac, and psychological stress on the dog.
Psychological Stress
When dogs have difficulty breathing while holding conventional bumpers in their mouths during training, this may cause them psychological stress. This is because when the trainer/owner places great physical demands on the dog, this can increase psychological stress and discomfort to the dog.
Conclusion
The use of conventional bumpers decreases a dog's ability to dissipate heat and to efficiently exchange oxygen and carbon dioxide, and increases cardiac output, intra-thoracic pressure, and psychological stress. Accordingly, it can be seen that needs exist for improvements to retrieval bumpers to decrease the thermal and psychological stress on the dog and to make the retrieving activity more comfortable, fun, and safe for the dog. It is to the provision of solutions meeting these and other needs that the present invention is primarily directed.